Soft contact composition and method

ABSTRACT

A soft contact lens is provided by: pouring an excess amount of an original solution for producing a soft contact lens into a concave mold; placing a convex mold on said concave mold and overflowing the excess of said original solution to thereby uniformly fill said original solution in a space between said concave mold and said convex mold; gelling said original solution between the two molds to form therebetween a lens having a tensile strength of at least about 0.1 kgf/cm 2  ; immersing said lens and said two molds in a liquid to peel said lens from said molds; and extracting the thus-peeled lens via an extraction treatment with water. The &#34;original solution&#34; contains: 
     a component A selected form the group consisting of monomers and hydrophilic polymers, wherein the monomers yield hydrophilic components when polymerized; a component B, which is a hydrophobic polymer having ethylenic double bonds in its side chains as post-cross-linkable groups, and a solvent C, 
     the weight ratio of A:B being from about 85:15 to about 55:45 and solvent C being about 5 to 95% by weight.

This application is a continuation of U.S. application Ser. No. 274,735,filed June 18, 1981, now abandoned, which is a division of applicationSer. No. 190,820 filed Sept. 25, 1980, now U.S. Pat. No. 4,347,198,which is a continuation of application Ser. No. 940,318, filed Sept. 7,1978, now abandoned.

SUMMARY OF THE INVENTION

The present invention provides a process for producing in a facilemanner a high-quality soft contact lens with little deviation in qualityat a high yield, and an "original solution" for producing the softcontact lens used in said process.

The present invention provides soft contact lens from an originalsolution that is filled into a concave and convex molds, the monomericand/or polymeric mixture being gelled, the resultant gelled polymer thenbeing peeled from the mold and finally extracted via water treatment.The "original solution" is a mixture of monomers and/or polymers morefully defined hereinafter together with a solvent and optionalingredients also set forth below, this "original solution" beingtransformed into the soft contact lens through filling it into theconcave and convex molds, preferably made of glass; polymerizing to agel; peeling; and finally extracting.

In its generic aspect, the invention provides a process for producingthe soft contact lens through pouring an excess amount of originalsolution for producing a soft contact lens into a concave mold; placinga convex mold on said concave mold and overflowing the excess of saidoriginal solution to thereby uniformly fill said original solution in aspace between said concave mold and said convex mold; gelling saidoriginal solution between the two molds to form therebetween a lenshaving a tensile strength of at least about 0.1 kgf/cm², immersing saidlens and said two molds in a liquid to peel said lens from said molds;and extracting the thus-peeled lens via an extraction treatment withwater.

In accordance with subgeneric aspects of the invention, the originalsolution has a coefficient of gellation contraction at the sametemperature and pressure of less than about 5% by volume. In oneembodiment of the invention, the original solution contains N-vinyllactam and a lower alkyl ester of acrylic acid or methacrylic acid. In afurther embodiment, the original solution contains a polymer of a loweralkyl ester of methacrylic acid having an ethylenic double bond in theside chain and N-vinyl lactam. The two molds are preferably made ofglass, and the convex mold preferably has a non-interference surface.

In a preferred embodiment, the gellation step is caused by heating. Apreferred embodiment of the peeling step utilizes a dimethylsulfoxide-water mixture.

The original solution is a component A selected from the groupconsisting of monomers and hydropholic polymers, wherein the monomersyield hydrophilic components when polymerized; a component B, which is ahydrophobic polymer having ethylenic double bonds in its side chains aspost-cross-linkable groups, and a solvent C,

the weight ratio of A:B being from about 85:15 to about 55:45 andsolvent C being about 5 to 95% by weight.

It is to be understood that the term "monomer" as defined above there isincluded the partially polymerized form which has not reached the stageof gellation, particularly with respect to the monomer component B.

Through the present invention it is possible to obtain a soft contactlens which is optically homogenous and without bubbles, despite theshape of the lens. Another problem that is avoided is the problem of"hollows", which may be caused through polymerization contraction. Insome prior art methods an original solution flows slightly inside themolds, so that a memory of such flow develops after the hydration. Afurther problem avoided by the present invention concerns the problemswith finishing lenses made by polymerization contraction, such finishingnot being required for the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The process for producing a soft contact lens according to the presentinvention consists mainly of the following four steps.

(1) a filling step

(2) a gellation step

(3) a peeling step

(4) an extracting step

In the filling step an original solution for producing a soft contactlens is filled in a space between concave and convex molds. The"original solution" contains the following components A, B and C, theratio of the component A to the component B ranges from about 85:15through about 55:45 and the content of the component C is about 5-95% byweight.

A. at least one kind selected from the group consisting of a monomerwhich gives a hydrophillic component when polymerized and a hydrophillicpolymer

B. at least one kind selected from the group consisting of a monomerwhich gives a hydrophobic component when polymerized and a hydrophobicpolymer

C. a solvent.

In addition to the above, a cross-linking agent may be used and apolymerization initiator may also be included.

As monomer of the component A there may be mentioned an N-vinyl lactamsuch as N-vinyl pyrrolidone, N-vinyl piperidone and N-vinyl caprolactam;N-vinyl oxazolidone; a hydroxy lower alkyl ester of acrylic acid ormethacrylic acid such as hydroxyethyl or hydroxypropyl ester of acrylicacid or methacrylic acid; glycerin monoacrylate or glycerinmonomethacrylate; and an ortho-lactone having a hydrophilic group. Asused above and throughout the description of the invention, as preferredlower alkyl may be mentioned alkyl of up to 6 carbon atoms.

The hydrophilic polymer of the component A is a cross-linkablehydrophilic polymer having functional group(s) adequate to form across-linkage between one hydrophilic polymer and another (postcross-linking). Illustrative of such hydrophilic polymer is the productobtained by (co)polymerizing one kind or at least two kinds of saidmonomer of the component A and, if necessary, a monomer for introducingfunctional group(s) to a polymer (functional group-introducing monomer).As said functional group-introducing monomers there may be mentionedn-butoxymethylacrylamide, glycidyl methacrylate, vinylene carbonate,hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl methacrylate,vinyl acrylate, methacrylic acid and acrylic acid. The copolymerizationratio of the monomer to the functional group-introducing monomer ispreferably within the range of about 1000:1 to about 10:1. Of thoseillustrated above especially preferred is the product obtained bycopolymerizing N-vinyl pyrrolidone as the monomer and vinylene carbonateas the functional group-introducing monomer.

As another example of such a hydrophilic polymer, polyvinyl alcohol maybe cited. In this case, hydroxyl groups in the polymer enable a postcross-linking reaction to take place; therefore, a new functional groupneed not be introduced. The post cross-linking reaction may be carriedout by using a polyvalent isocyanate, a polyvalent aldehyde and methylolmelamine as a post cross-linking agent.

Said monomer which when polymerized, gives a hydrophobic component ofthe component B points to what is not cross-linked when it is made ahigh molecular weight substance, yet neither swells nor dissolves inwater. As such monomer, there may be cited a lower alkyl ester ofacrylic acid or methacrylic acid (for example, methyl methacrylate); anunsaturated nitrile such as acrylonitrile or methacrylonitrile; anaromatic olefin such as styrene and a hydrophobic ortholactone.

When monomers are used as said component A and said component B, it isdesirable that one monomer is unlikely to be copolymerized with theother monomer, and it is also desirable that monomer reactivity ratiosare:

    1/r.sub.A >1 and 1/r.sub.B >1

(wherein r_(A) is a reactivity ratio of the monomer of the component Ato the monomer of the component B, and the ratio of the possibility thatA is added to an A-terminated polymer to the possibility that B is addedthereto; r_(B) is a reactivity ratio of the monomer of the component Bto the monomer of the component (A). In this case, when acrylic acid ormethacrylic acid is added in an amount up to about 5% by weight based onthe entire monomers as a third monomer component, it becomes possible toraise the water content without lowering the tenacity of the lens.

Said hydrophobic polymer of the component B points to a cross-linkablepolymer having functional group(s) adequate for forming a cross-linkagebetween one hydrophobic polymer and another (post cross-linking) andneither swells nor dissolves in water. Representative of suchcross-linkabe hydrophobic polymer is the product obtained by(co)polymerizing one kind or at least two kinds of said monomer of thecomponent B and, if necessary, said functional group-introducingmonomer. It is preferable that the copolymerization composition ratio ofthe monomer to the aforesaid functional group-introducing monomergenerally ranges from about 1000:1 to about 10:1. As a hydrophobicpolymer, a non-cross-linking polymer, for example, polyvinyl butyral maybe mixed.

In both cases of polymers of the component A and the component B, when ahydroxyl group is contained as a functional group, it is possible tomake said polymer, a post-cross-linkable polymer by esterifying saidhydroxyl group with, for example, methacrylic acid to thereby introducean ethylenic double bond to the side chain. As to combination of thecomponent A with the component B, such combination as to give anoriginal solution whose coefficient of gellation contraction at the sametemperature and the same pressure (hereinafter referred to as γ_(o)) isless than about 5% by volume, is preferable. More specifically, thereare the following preferable combinations.

(1) Combination of monomers used both as the component A and thecomponent B:

N-vinyl lactam, especially N-vinyl pyrrolidone as the component A.

A lower akyl ester of acrylic acid or methacrylic acid, especiallymethyl methacrylate as the component B.

(2) Combination of a monomer used as the component A with a polymer usedas the component B:

N-vinyl lactam, especially N-vinyl pyrrolidone as the component A.

A polymer having an ethylenic double bond in the side chain, obtained byreacting (esterifying) methacrylic acid with a lower alkyl ester ofmethacrylic acid (especially, methyl methacrylate)glycidyl methacrylatecopolymer, or a non-gelled copolymer of methyl methacrylate and vinylmethacrylate as the component B.

(3) Combination of polymers used both as the component A and thecomponent B:

A polymer obtained by reacting (esterifying) methacrylic acid with ahydrolyzed N-vinyl pyrrolidone-vinylene carbonate copolymer as thecomponent B.

A non-gelled copolymer of methyl methacrylate and vinyl methacrylate asthe component B.

(4) Combination of a post cross-linkable polymer and a monomer used asthe component A and a monomer used as the component B:

This combination is effective because it imparts a proper viscosity toan original solution for polymerization.

Of the foregoing, what is especially preferable is combination ofN-vinyl pyrrolidone with methyl methacrylate.

It is necessary that the mixing ratio of the component A to thecomponent B should range from about 85:15 to about 55:45. In case theamount of the component A exceeds the upper limit of said range, viz.about 85%, a high-tenacity lens cannot be obtained, and in case theamount of the component A becomes less than about 55%, a lens having ahigh water content cannot be obtained. If said ratio is within theaforesaid range, a lens having a high tenacity and a high water contentthat are well balanced is obtainable.

The solvent component C must be one that does not obstruct thepolymerization reaction and the post cross-linking reaction, and suchsolvent as to give a transparent original solution is preferable. When asolvent giving an opaque original solution is used, the lens isunsatisfactory in optical properties, and also in many cases in dynamicproperties.

In case both the component A and the component B are monomers, it is notnecessarily required that a solvent be used which is capable ofsimultaneously dissolving polymers of the two components. Insofar as itis a solvent dissolving either one of the two components, any solventmay be usable. It is possible to select a solvent from a wide rangedepending upon combination of the component A with the component B. Incase N-vinyl pyrrolidone is combined with methyl methacrylate, which isan especially preferable mode of practice of the present invention thereis preferably used dimethyl sulfoxide and/or ethylene carbonate or anorganic solvent system obtained by adding a small amount of dioxane tothem. In case a polymer of N-vinyl pyrrolidone is used as the componentA and a polymer of methyl methacrylate is used as the component B,dimethyl formamide, N-methyl pyrrolidone and dimethyl acetamide they maybe used as a solvent, as they simultaneously dissolve the two polymers.

It is necessary that the amount of the solvent used be within the rangeof about 5-95% by weight based on the total amount of the originalsolution; of said range, the range of about 30-90% by weight ispreferable, and the range of about 50-90% by weight is most preferable.In case the amount of the solvent exceeds about 95% by weight, thetensile strength of a solvent-containing gel obtained by polymerizingand/or cross-linking the original solution becomes low, therefore,handling of the solvent-containing lens becomes somewhat difficult.

It is preferable to so adjust the original solution as to make thetensile strength of a solvent-containing gel, not less than about 0.1 kgf/cm² ; and for that end, it is necessary not only to make the amount ofthe solvent within the aforesaid range, but also to carefully select thekind of solvent. When the amount of the solvent becomes less than about5% by weight, a hydrated lens upon swelling is hard, the water contentof the lens becomes low or the lens undergoes permanent deformation tosuch an extent that parts of the molecules are destroyed due to aswelling force. What is most preferable is that dimensional changebrought about when a solvent contained in a gel is substituted by water,is within the range of from about +20% through about -30%.

The cross-linking agent will now be considered: When a polymer is usedas the component A or B, post cross-linking agent reacting with thefunctional group(s) of the polymer to form cross-linkage between onepolymer molecule and another, is used as occasion demands. As a postcross-linking agent, whatever substance is usable unless it changesessentially the properties of the polymer. For a polymer containinghydroxyl group(s) as a functional group, a polyvalent isocyanate, apolyvalent aldehyde and a polyvalent carboxylic acid ester are usable asa post cross-linking agent. When a polymerizable monomer is used as thecomponent A or B, a cross-linking agent is added to advance across-linking polymerization. The cross-linking agent is selected fromcompounds each having at least two polymerizable unsaturated bonds inthe same molecule.

As such cross-linking agents, may be mentioned di- or tri-allylcompounds such as diallyl succinate, diallyl phthalate, diallyl maleate,diethylene glycol bis-allyl carbonate, triallyl cyanurate, triallylisocyanurate, triallyl phosphate and triallyl trimellitate; a di- ortri-vinyl compound such as divinyl benzene, N,N'-methylene bisacrylamide, (poly)ethylene glycol dimethacrylate, hexamethylene bismaleimide, divinyl urea, bisphenol A bis methacrylate, divinyl adipate,glycerin trimethacrylate, trimethylol propane triacrylate, trivinyltrimelitate and 1,5-pentadiene; an allylvinyl compound such as allylacrylate and allyl methacrylate; and vinyl (meth)acrylate. The amount ofsuch cross-linking agent to be added is within the range of about0.005-20 mol % based on the total amount of the polymerizable monomersof the component A and the component B.

A cross-linking polymerization is carried out by such means as heat,rays and electronic rays in the presence of a polymerization initiationif necessary. As preferred examples of such a polymerization initiator,there may be mentioned an organic peroxide such as di-tert-butylperoxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylhydroperoxide, tert-butyl perpivalate, peracid and ammonium persulfate;an azo compound such as azobisisobutyronitrile, azobiscyclohexanecarbonitrile, phenylazoisobutyronitrile andazobis-dimethylvaleronitrile; and a redox catalyst. The amount of suchpolymerization initiator to be added is within the range of about0.001-3% by weight based on the polymerizable monomer.

It will be seen by a worker skilled in the art that in addition to thecriteria previously set forth, additives such as a cross-linkingpromotor and coloring agents may be added to the original solution ofthe present invention as needed. It is also possible to add a polymerwhich can be extracted from a solvent-containing gel to the originalsolution, for example, poly N-vinyl pyrrolidone. Not only such anextractable polymer, but also an extractable substance may be formallyregarded as a part of the solvent.

The smaller is the γ_(o) of the original solution, the more preferableit is. When a casting method is adopted in which the volume of alens-shape space gradually decreases as contraction due topolymerization proceeds, even though the value of γ_(o) is 15-20%, thereis no possibility that hollows are brought about. However, in case thediopter of a lens is a large positive or negative value, the thicknessof a lens-shape space varies depending upon the place, and so theoriginal solution slightly flows and the memory of such flow developsafter a hydration treatment, which is not desirable. From thisviewpoint, it is preferable that γ_(o) is less than about 10% by volume,and still more preferably less than about 5% by volume.

As preferred embodiments of compositions original solutions forproducing a soft contact lens of the present invention may be mentioned:

(1) The combination, wherein N-vinyl pyrrolidone and methyl methacrylateare used as monomers, of triallyl isocyanurate, triethylene glycol andvinyl methacrylate are used as cross-linking agents, azobisdimethylvalerolactam is used as a catalyst and dimethyl sulfoxide is used as asolvent.

(2) The combination, wherein N-vinyl pyrrolidone is used as a monomer, anon-gelled copolymer of methyl methacrylate and vinyl methacrylate isused as a post cross-linkable polymer, triallyl isocyanurate is used asa cross-linking agent, azobisdimethyl valeronitrile is used as acatalyst and dimethyl sulfoxide is used as a solvent.

(3) The combination, wherein a post cross-linkable polymer obtained byhydrolyzing a vinyl pyrrolidone-vinylene carbonate polymer andthereafter esterifying the resultant hydrolyzed copolymer withmethacrylate acid and a non-gelled copolymer of methyl methacrylate andvinyl methacrylate are used as polymers and N-methyl pyrrolidone is usedas a solvent.

Two kinds of molds are used in the present invention, a concave mold anda convex mold. At least one of the these two molds should have aninterference surface, whether spherical or paraboloidal, defining a lenssurface. The term "interference surface" herein refers to a generallyspherical or paraboloidal surface which has a surface roughness in itscentral, primary portion of not more than 50 μm and which in itscircumferential, peripheral portion deviates or projects from a truespheroid or paraboloidal properties at that circumferential portion. Amold having a "non-interference" surface, as that term is used herein,is spherical or paraboloidal over the entire surface which acts todefine a lens surface when the concave and convex molds are contacted asdescribed below. It is preferable that the concave mold and the convexmold are so designed as to bring them into a linear, not surfacecontact.

Examples of combination of a concave mold and a convex mold used in thepresent invention will be explained by reference to the accompanyingdrawings.

FIG. 1 is a combination of a concave mold having an interference surface1 with a convex mold having a non-interference surface 2 which is aspherical surface or paraboloid surface having no projections. Thiscombination is especially preferable for practicing the presentinvention. This is because the concave mold having n interferencesurface is used, a lens through which tear flows well is produced, andan inner bevel (an inclined surface produced on the circumferentialportion on the side of the concave surface of a lens, which has beenalmost indispensable for wearing a conventional contact lens) is notproduced (in the case of a soft contact lens obtained by the process ofthe present invention, no problem is brought about for wearing such alens even though there is no inner bevel), it is possible to easilyproduce a contact lens high in general usability with little deviationin quality.

FIG. 2 is an example of combination of a concave mold having aninterference surface 1 with a convex mold also having an interferencesurface 4, by the use of such molds, the present invention can be easilypracticed also. As a concave mold, what has a non-interference surfacemay also be used, however, except for a special mold, an outer bevel (aninclined surface produced on the circumferential portion on the side ofthe convex surface of a lens) is generally necessary, therefore, aconcave mold having an interference surface is preferably used. On thecircumferential portion of the mold surface of a convex mold, a thingroove or small hole may be produced, which results in producing aprojection on the circumferential portion on the side of the concavesurface of the lens and promoting flow of tear. When a hole is marked,such marked hole is also utilizable for identification of the kind. Thematerial of a mold may be made of plastic, metal or glass, preferablyglass.

FIG. 3 is an example of a combination of a concave mold having aninterference surface 1 with a convex mold also having an interferencesurface 4. This combination is excellent in that a lens flash producedin the overlapped surface of the molds does not contact the cornea. Thiscombination is especially suitable for manufacturing a mold from athermoplastic plastics or a metal by a transcription method.

In the filling step, an original solution in an excess amount is pouredinto a concave mold. Pouring of the excess amount is not only necessaryfor uniformly filling the original solution neither more nor less in aspace between the concave mold and a convex mold, but also important inthe following sense. Namely, in the molds shown in FIG. 1 which ispreferable for practicing the process of the present invention, becausethere is a wedge-like space 3 in a sealed portion, an overflowedoriginal solution is held at that space 3 to make complete the sealing.On the other hand, when polymerization contraction is brought about, theoverflowed original solution is supplied from a slight gap in the sealedportion to make up for the polymerization contraction. In case suchmolds are used, an amount about 5 times or more of the amount of theoverflowed original solution held in said wedge-like space had better bemade an excess amount of the original solution. Determination of thecharging amount of the original solution may also be practiced asfollows. Namely, a plurality of molds each charged with the originalsolution are placed, when necessary, in a sealed vessel in which air isreplaced by an inert gas such as nitrogen for transferring said molds toa gel producing step, at this time, the vapor pressure of the lowestboiling point component in the original solution inside said vessel isso established as to become at least about 20% of the saturated partialpressure exhibited by the original solution. By charging such an excessof the original solution, it becomes possible to prevent a lens fromenfolding bubbles and inhibit delicate change of composition of theoriginal solution inside each mold during production of gel to enable avery high-quality lens to be obtained at a good yield.

Another mode of practice of the filling step is to fill the originalsolution in a sealed container. Namely, a concave mold is placedstationarily in a sealable container, the original solution is pouredinto the concave mold, thereafter, the entirety is inclined for placinga spherical convex mold in said container, air inside the container isdegasified or replaced by an inert gas as occasion demands, andthereafter the container is sealed and lightly shaken to partly fit theconvex mold in the concave mold.

In a gellation step, a polymerization and/or cross-linking reaction iscaused to proceed by the action of heat, rays and electronic rays. Whensuch reaction is caused by heat, said reaction is carried out normallyat a temperature within the range from room temperature through about120° C.

There are the following five practical methods for not producing holesand hollows by polymerization contraction of the original solution.

(a) A liquid is supplied from an overlapped surface of the concave andconvex molds.

(b) Pressure acting on the original solution and/or gel in a spacebetween the concave and convex molds is reduced to develop elasticexpansion.

(c) The original solution and/or gel in a space between the concave andconvex molds is heated to develop thermal expansion.

(d) A hole and/or hollow is produced at a position other than theoptical area (an area within a circle having a radius within about 4 mmcentering around the optical axis) in a space between the concave andconvex molds.

(e) The volume V of the space between the concave and convex molds issomewhat decreased during a process from initiation through terminationof the polymerization reaction.

When, as mentioned above, the overflowed original solution is held in asealed portion of the molds, in case the pressure inside the moldsbecomes minus by polymerization contraction, the original solution isnaturally absorbed from the overlapped surface of the two molds, bywhich the method (a) is realized. This method is preferable in a metalmold rather than in a plastic mold and most preferable in a glass mold.In the case of glass molds, a gap on the overlapped surface becomeslarge sometimes, in such case the concave and convex molds are squeezedfrom up and down with a force of 10-200 kg f, preferably about 50 kg f.

The liquid to be supplied is an overflowed original solution in theaforesaid case, however, it is not limited to the original solution, buta monomer and a solvent will suffice.

The original solution is sealed in a pressurized, compressed statewithin the molds and as the polymerization proceeds, the internalpressure automatically lowers, by which the method (b) is achieved.

The original solution is pressurized by heating and pressing in by apump of the original solution in a sealed space.

For sealing the overlapped surface of the concave and convex molds, whensqueezing of the concave and convex molds from up and down results inincomplete sealing, the concave and convex molds are placed inside anautoclave and the original solution is filled outside these molds alsobut inside said autoclave, by which a satisfactory result is obtained.

The method (c) is achieved by gradually elevating the temperature of theoriginal solution as polymerization progresses.

The thermal expansion coefficient of a monomer is not large, however,the following two solutions are effective. One is to mix the monomerwith a solvent large in thermal expansion coefficient and carry out asolution polymerization. The other is to carry out a reaction attemperatures ranging from a low temperature immediately before freezingthrough a high temperature immediately before decomposition. In thiscase, because a proper thermal polymerization catalyst is not obtained,an electron ray polymerization is desirable.

The method (d) is to eliminate overall contraction of the entirety bybringing about hollows in harmless positions. Such positions are anouter bevel or an inner bevel of a lens. In order to continuouslyproduce hollows in that positions, foaming nuclei had better be providedon the outer bevel portion of the concave mold. As such foaming nuclei,a rough surface of the molds, contamination caused by foreign matterssuch as a very small amount of oil or grease and a plastic fiber arepreferable.

The method (e) is achieved by gradually decreasing the volume of alens-shape space V as polymerization proceeds.

When the decreasing amount of V during the polymerization is named ΔV,up to about ΔV/V=3% can be practiced the process of the presentinvention. In the case of glass molds, when an assembly of concave andconvex molds is squeezed by a force of about 100 kg f, a volume decreaseof about 2% is achieved.

Of the foregoing methods, what is preferable in performance of anobtained lens is (a), (b), and (c), and (d) and (e) had better be usedas auxiliary means. These methods are used in proper admixture.

Peeling of a solvent-containing gel from molds had better be carried outin a liquid, especially in an aqueous solution, Namely, an assembly ofthe concave and convex molds per se is immersed in the liquid. Sincecontact of the overlapped surface of said assembly with the liquid wouldsuffice, the entire molds need not be immersed. By peeling in theliquid, it is possible to drastically reduce the damaging ratio of alens. This effect is especially remarkable when glass molds are used.

When peeling operations are carried out in water, substitution of asolvent contained in the gel with water could be continuously carriedout per se.

The liquid used upon peeling is not particularly limited insofar as itdoes not adversely affect the lens, however, in general, a solvent thesame as used in the original solution added with water is preferablyused. In case N-vinyl pyrrolidone is selected as the component A andmethyl methacrylate is selected as the component B of the originalsolution, peeling had better be carried out in dimethyl sulfoxide orwater. These may be called solvents weaker in action for swelling thegel than the solvent contained in the original solution.

An extraction step is a step of subjecting the peeled lens to anextraction treatment with water (including physiological saline andother aqueous solutions). At this time, the monomer(s), polymer(s),cross-linking agent, catalyst and solvent elute, while water and anartificial tear solution flow in.

When this step is completed, a hydrated gel whose percent transmissionof visible rays is more than about 90% per thickness of 0.1 mm, isobtained.

EXAMPLE 1

A concave mold used in this example is made of a low-pressurepolyethylene, having a shape like 1 of FIG. 2, the radius of curvatureand the diameter of which are 7.5 mm and 13 mm, respectively. A convexmold used in this example is a glass ball having a radius of curvatureof 8 mm. A gap in the central portion(s) is 0.9 mm.

Composition of an original solution for polymerization is a mixture ofhydrophilic monomers and solvents as shown below.

hydroxyethyl methacrylate (HEMA)--70 g,

N-vinyl pyrrolidone (NVP)--30 g,

acrylic acid--2 g,

ethyleneglycol dimethacrylate (EGDMA)--1.5 g,

triallyl isocyanurate (TAIC)--0.5 g,

ammonium persulfate--2 g,

ethylene glycol--150 g,

water--150 g.

The original solution in an amount in excess by 20 μl was poured intothe concave mold and the convex mold was carefully placed thereon aroundthe center of the former. Because the excess amount of said solution wasconsiderably large, a probability of enfolding bubbles was low.

The two molds were clamped by a force of 0.5 kgf and the originalsolution was polymerized inside a hot air oven, said solution was heatedat 60° C. for 16 hours and then at 90° C. for 4 hours. The γ_(o) of theoriginal solution was 3.5%, a greater part of which, however, was madeup for by reduction of the volume of the molds.

After immersing an assembly of the two molds in water, the clamps wereloosened, said assembly was allowed to stand for overnight per se inwater and the two molds were separated in water. By so doing, a ratio ofbreaking the circumference of the lens decreased by about 10% ascompared with a case of loosening the clamps in air and separating thetwo molds in air.

Because a lens adhered to the concave mold, when said mold was allowedto stand in water for 5 hours, the lens naturally peeled from said mold.

The water content was about 75% in water at pH 8 and the lens havingnon-destroyed edge was obtained. The percent transmission of rays was85%.

In order to know the approximate value of the tensile strength of thesolvent-containing lens, after being heated at 90° C. for 4 hours, thelens was taken out into air, the convex mold was separated from theconcave mold and the lens was peeled by a pair of tweezers. From thefinger touch at that time, the tensile strength of the lens was inferredto be about 2-0.5 kgf/cm².

EXAMPLE 2

Using the same molds and the same original solution as used in Example1, the original solution was charged by the same method, thereafter, thetwo molds were clamped by a force of 0.5 kgf and the original solutionwas polymerized in water. After heating the two molds under the sameconditions as in Example 1, the clamps per se were loosened in water,the two molds were allowed to stand in water for overnight andthereafter the two molds were separated. A lens whose edge was littledestroyed was obtained.

EXAMPLE 3

A concave mold used in this example was a non-interference sphere madeof glass having a radius of curvature of 7 mm and a diameter of 13 mm. Aconvex mold used was the same as that used in Example 1. The gap in thecentral portion(s) was 1 mm. At the contact portion of the two molds, awedge-like space like 3 in FIG. 1 was provided. Both of the two moldsbeing non-interference spherical surface, a lens becomes a thick concavelens having a crescent-like sectional configuration.

Composition of an original solution for polymerization was as follows, amixture of a hydrophilic monomer, a hydrophobic monomer and a solvent.

NVP--70 g,

methyl mechacrylate (MMA)--30 g,

TAIC--1 g,

triethyleneglycol dimethacrylate (TEGDMA)--3 g,

vinyl methacrylate (VMe)--0.5 g,

azobisdimethyl valeronitrile (ADVN)--0.1 g,

dimethyl sulfoxide (DMSO)--400 g.

The γ_(o) of this original solution was about 3.5%.

The concave mold was placed inside a high-rigidity, pressure-resistant5000 kgf/cm² autoclave, the original solution was overflowingly pouredinside the autoclave and the autoclave was covered. Heating was effectedat 40° C. until 9.5th hour, 50° C. until 11.2th hour, 60° C. until13.7th hour, 70° C. until 14.1th hour, 80° C. until 14.9th hour,thereafter the autoclave was smoothly heated at 90° C. until 15.8thhour, and thereafter the autoclave was allowed to stand until 18th hour.While care was taken so as not to cool the autoclave, an assembly of theconcave mold and convex mold was quickly taken out and immediatelyimmersed in a treating liquid. The treating liquid was a 70% aqueoussolution of DMSO (at 95° C.), after 5 hours, the convex mold wasseparated from the concave mold, said concave mold was immersed in a 10%aqueous solution of DMSO (at 95° C.) for 5 hours. During the period, alens naturally peeled from the concave mold. Although the circumferenceof the lens was very thin, the lens free from damage was obtained. Whenthe lens was boiled in water for overnight, it became a transparent softcontact lens.

In order to know the approximate value of the tensile strength of thesolvent-containing lens, the concave and convex molds taken out from theautoclave were separated in air and the solvent-containing lens waspeeled by a pair of tweezers. From the finger touch at that time, thetensile strength of the lens was inferred to be about 1-0.1 kgf/cm².

The hydrated lens had a water content of 75%, a percent transmission ofrays of 85% and a tensile strength of 4 kgf/cm².

EXAMPLE 4

An experiment showing toughness of a pressure polymerization was carriedout. The temperature elevation program of Example 3 was changed toelevation of temperature at a slow speed, which was made an optimumvalue in an atmospheric pressure polymerization shown in Example 5.

Increase of a hollow occurring ratio due to polymerization contractionwas hardly recognized. Number of flashes brought about in the overlappedsurface of the two molds was rather small. This was recognized to be theslowest speed temperature elevation. The pressure inside a space betweenthe molds at this time was inferred to be always close to atmosphericpressure. Accordingly, the inner pressure in Example 3 is guessed tohave been considerably high.

As such, in a pressure polymerization, the range which could be taken bythe temperature elevation program is broad, which is contrastive todelicacy of a pressure polymerization inferred from Example 5.

EXAMPLE 5

Molds the same as used in Example 3 were used. A concave mold was placedhorizontally on the bottom of an autoclave in advance, on which wasplaced a convex mold, from the overlapped surface of the two molds, aneedle was inserted to inject about 1 ml of an original solution thesame as used in Example 3 and the needle was pulled out. Bubbles werehardly enfolded. The overflowed original solution wetted thecircumference of the concave mold to say nothing of a wedge-like space,being accumulated on the bottom of the autoclave. The autoclave wasfilled with nitrogen gas and covered. The inside of the autoclave mustbe filled with the vapor of the original solution.

A polymerization was carried out according to the following temperatureelevation program, connecting smoothly the following temperatureelevation curve.

Until 81/4th hour--39° C.,

At 91/4th hour--46° C.,

At 101/4th hour--50.5° C.,

At 111/2th hour--54° C.,

At 12th hour--56° C.,

At 121/2th hour--60° C.,

At 13th hour--74° C.,

At 14th hour--84.5° C.,

From 141/2th hour through 16th hour--90° C.

The steps thereafter were the same as those in Example 3.

An obtained lens was, the same as in Example 3, low in damaging ratiowith few hollows, having about the same values of the physicalproperties. This temperature elevation program was the values inatmospheric pressure polymerization and when the temperature changed by±3° C. (for over 10 minutes) from the values mentioned above, a lenswith many hollows and (flange-like projections) tended to be produced.

EXAMPLE 6

A part of Example 5 was charged. Namely, after squeezing the assembly ofthe concave mold and the convex mold with an outer force of 50 kgf, theautoclave was covered.

A temperature elevation program the same as in Example 5 was optimum,however, it was seen that a more severe precision was required in thisexample as compared with that of Example 5.

Number of flashes in the circumference of an obtained lens was small.There were no large difference in damaging ratio in concomitance withpeeling, occurring ratio of hollows and value of the physical propertiesbetween the lens of this example and the lens of Example 5.

EXAMPLE 7

A concave mold used in this example was made of glass, having aninterference spherical surface like that of 1 in FIG. 1, having a radiusof curvature of about 9 mm and a diameter of 13 mm. Because said moldwas manufactured manually by fire forging, the precision of the opticalsurface was very poor. As a convex mold, what was used in Example 1 wasused. The gap in the central portion(s) was about 0.4 mm.

Composition of an original solution for polymerization was, as shownbelow, a mixture of a hydrophilic monomer, a post cross-linkablehydrophobic polymer and a solvent.

post cross-linkable polymethyl methacrylate (PMMA*)--28 g,

NVP--75 g,

TAIC--1 g,

ADVN--0.1 g,

DMSO--416 g.

Using this original solution for polymerization, by the method ofExample 5, a polymerization was effected. The solvent contained in anobtained lens was substituted with water (allowed to stand in boilingwater for 16 hours), thereafter said lens at 37° C. was a welltransparent soft contact lens-like matter having a water content ofabout 80% and a tensile strength of about 10 kgf/cm².

Said post cross-linkable polymethyl methacrylate was synthesized by thefollowing method.

MMA--99 g,

VMe--1 g,

ADVN--0.1 g,

DMSO--400 g.

A composition consisting of the aforementioned components was charged ina 1-liter 3-neck flask equipped with a stirrer, air inside said flaskwas substituted by argon, thereafter, said composition in said flask wasstirred inside a 50° C. water vessel to precipitate a viscous solutionin a state of very fine powder. The precipitate was removed of thesolvent by centrifugation, thereafter, washed twice with fresh methanol,dried in vacuo at a temperature not more than 40° C. for about 24 hoursuntil the amount thereof became constant, and what was obtained wasused.

The obtained polymer had an [η]÷0.8 and the yield was about 30 g.

EXAMPLE 8

In the process of Example 7, what was synthesized by the followingmethod was used as a post cross-linkable polymer.

MMA--95 h,

glycidyl methacrylate (GMA)--5 g,

ADVN--0.6 g,

n-dodecylmercaptan (n-DSH)--0.14 g,

DMSO--233 g.

A composition consisting of the aforesaid components was polymerized at50° C. for 9.5 hours in the same manner as the synthesis of a polymer inExample 7. An obtained polymer was refined and dried. The resultingpolymer had a yield of about 33 g and an [η]÷0.5.

In order to add methacrylic acid to this polymer, the following reactionwas carried out.said polymer 10 gmethacrylic acid (MeAA) 6 gtrimethylbenzylammonium chloride 1 g(TMBAC) ##STR1## 0.05 g1,2-dichloroethane 80g______________________________________

A composition consisting of the aforesaid components was charged in a300-ml, 3-neck flask equipped with a stirrer. Said composition in saidflask was reacted in a water vessel at 80° C. for 8 hours. After thereaction, an obtained reaction product was precipitated so as to becomevery fine powder in methanol, removed of the solvent by centrifugation,thereafter washed twice with methanol and used for a polymerization. Asa result of examining by a method of nuclear magnetic resonance, about3% (weight in the polymer) of methacrylic group was contained.

As a result of measurement of viscosity, the resultant polymer exhibitedabout the same viscosity as that of the starting polymer. The obtainedlens after substitution of the solvent contained by water had a somewhatweaker tensile strength, but it gave a well transparent lens-likematter.

EXAMPLE 9

In Example 7, the cross-linking agent in the original solution for apolymerization only was changed. Namely, composition of the originalsolution was as follows.

PMMA*--28 g,

NVP--75 g,

ethylidene-bis-3-(N-vinyl-2-pyrrolidone) (ENVP)--1 g,

ADVN--0.6 g,

DMSO--416 g.

The obtained lens after its solvent was substituted by water was alens-like matter high in transparency than that of Example 7.

EXAMPLE 10

In Example 8, only the cross-linking agent in the original solution fora polymerization was changed. Namely, composition of the originalsolution was as follows.

PMMA*--28 g,

NVP--75 g,

MeV--1 g,

ADVN--0.1 g,

DMSO--416 g.

The obtained lens after its solvent was substituted by water was alens-like matter as transparent as that of Example 7.

EXAMPLE 11 Method of synthesizing post cross-linkable polyvinylpyrrolidone

N-vinyl pyrrolidone and vinylene carbonate were polymerized.

NVP--29.1 g,

vinylene carbonate (VCa)--0.9 g,

ADVN--0.03 g,

benzene--70 g.

An original solution for a polymerization consisting of the aforesaidcomponents was put in a 300-ml, 3-neck flask equipped with a stirrer,air inside the flask was substituted by argon, and said solution waspolymerized with stirring at 50° C. for 7 hours.

After the polymerization, a polymer was precipitated in petroleumbenzine.

The polymer was dried in vacuo at 70° C. and the yield was 14 g.

Six grams of the obtained polymer was dissolved in 100 g of a 40%aqueous solution of hydrazine, allowed to stand at room temperature for3 days, thereafter removed of water by an evaporator, further dissolvedin water, and thereafter hydrazine was completely removed therefrom byan ion exchange resin.

After removal of hydrazine, the polymer was dehydrated by the evaporatorand further dried in vacuo. Four grams of the dried polymer wasdissolved in 50 g of dried methylene chloride, into the resultantsolution was added dropwise a mixture of 2 g of methacrylic acidchloride and 8 g of dried methylene chloride at room temperature withstirring. After completion of the dropping, the resultant mixture wasallowed to stand with stirring for 2 hours to precipitate in petroleumbenzine.

The obtained polymer was measured with methanol heavy hydride being usedas a solvent to confirm that a methacrylic acid group was introduced.

What is claimed is:
 1. An original solution for producing a soft contactlens comprising:A. a hydrophilic polymer or monomer that, whenpolymerized, gives a hydrophilic polymer; B. a hydrophobic polymer of amonomer selected from the group consisting of a lower alkyl ester ofacrylic or methacrylic acid, an unsaturated nitrile, an aromatic olefin,a hydrophobic ortho-lactone, a glycidyl ester of acrylic or methacrylicacid and a mixture thereof or a hydrophobic copolymer of said monomerwith a compound selected from the group consisting of acrylic acid,methacrylic acid, a vinyl ester of acrylic acid and a vinyl ester ofmethacrylic acid; said hydrophobic polymer or copolymer having aplurality of side chains, each side chain containing a postcross-linkable group; and C. a solvent wherein the weight ratio of A:Bis from about 85:15 to about 55:45 and C is present in a quantity offrom about 50 to 95% by weight, based on the original solution.
 2. Anoriginal solution of claim 1, wherein said monomer of the component A isN-vinyl lactam, N-vinyl oxazolidone, a hydroxy lower alkyl ester ofacrylic acid, a hydroxy lower alkyl ester of methacrylic acid, glycerinmonoacrylate, glycerin monomethacrylate or a hydrophilic ortho-lactone.3. An original solution of claim 1, wherein said hydrophilic polymer ofthe component A is (i) a polymer consisting of at least one kind ofmonomer selected from the group consisting of N-vinyl lactam, N-vinyloxazolidone, a hydroxy lower alkyl ester of acrylic acid, a hydroxylower alkyl ester of methacrylic acid, glycerin monoacrylate, glycerinmonomethacrylic and a hydrophilic ortho-lactone or (ii) a polymerobtained by introducing a post cross-linkable functional group topolyvinyl alcohol.
 4. An original solution of claim 1, wherein saidhydrophilic polymer of the component A is that which is obtained byhydrolyzing an N-vinyl pyrrolidone-vinylene carbonate copolymer andthereafter reacting the hydrolyzed copolymer with methacrylic acid. 5.An original solution of claim 1, wherein said hydrophobic polymer of thecomponent B is a polymer obtained by reacting a copolymer of a loweralkyl ester of acrylic acid or methacrylic acid, an unsaturated nitrile,an aromatic olefin or a hydrophobic ortho-lactone and glycidyl ester ofacrylic acid or methacrylic acid with acrylic acid or methacrylic acid.6. An original solution of claim 1, wherein said hydrophobic polymer ofthe component B is a polymer obtained by copolymerizing a lower alkylester of acrylic acid or a lower alkyl ester of methacrylic acid, and avinyl ester of acrylic acid or a vinyl ester of methacrylic acid, andstopping the polymerization before the obtained polymer gels.
 7. Anoriginal solution for producing a soft contact lens which comprisesN-vinyl pyrrolidone, a methyl methacrylate-glycidyl methacrylatecopolymer which is esterified with methacrylic acid and/or a methylmethacrylate-vinyl methacrylate copolymer, triallyl isocyanurate,azobisdimethyl valeronitrile and dimethyl sulfoxide.
 8. An originalsolution for producing a soft contact lens which comprises a hydrolyzedcopolymer of N-vinyl pyrrolidone and vinylene carbonate which isesterified by methacrylic acid, a methyl methacrylate-glycidylmethacrylate copolymer which is esterified by methacrylic acid and/or amethyl methacrylate-vinyl methacrylate copolymer, triallyl isocyanurate,azobisdimethyl valeronitrile and N-methyl pyrrolidone.
 9. An originalsolution of claim 1, wherein the B component is a hydrophobic polymerhaving plural ethylenic double bonds in its side chains aspost-cross-linkable groups.
 10. An original solution of claim 1, whereinthe B component is obtained by radical polymerization.